As Bitcoin, the math-based currency that enthusiasts say could revolutionize online transactions, becomes more mainstream, its supporters have been looking for ways to make it more accessible to investors. Today SecondMarket, a platform where privately-held or growth-stage companies can raise capital, says it is now offering a new Bitcoin Investment Trust . It’s an open-ended fund that lets institutional and accredited investors dabble in the crypto-currency without necessarily having to go through the headache of managing wallets or direct transactions. It invests exclusively in Bitcoin and investors who buy shares in the trust will be able to gain liquidity through regular auctions beginning next year on SecondMarket. Unlike the exchange-traded fund that Tyler and Cameron Winklevoss have been exploring, this one is only available to accredited investors, who are required...